Be very careful about this.
Elderly people, no matter how active and independent in life, can get progressively infirm.
If your mother had a stroke, got dementia etc she could become doubly incontinent, her personality can change and need full time care. Care home fees cost £1300 a week plus.
The responsibility and stress for providing full time care 24/7 on you and your family would be extreme.
Houses can be fitted with special steps, bath rails, stairlifts etc but if your mum became immobile and needed a wheelchair and was unable to use the bathroom unaided, you are going to have to think through the practicalities.
Getting carers in is also expensive and not always satisfactory.
Sorry this all seems to be a downer but a lot of people have a romantic notion of granny moving in and eventually passing away happy and surrounded by loved ones with being independent and able to do things, look after herself until passing away peacefully in her sleep.
Unfortunately this is not the reality 85% of the time.
Once someone loses their mobility it's a game changer.
If they regularly go for walks and hike, are sociable, have a real zest for life, have good hand eye coordination, good memory, good hearing, good eyesight, good sense of humour then go for it if you must.
Otherwise not a good idea.